Noise Floor
Understanding the Noise Floor
The noise floor is the ultimate sensitivity limit of any receiver or measurement instrument. Every signal below the noise floor is buried in noise and undetectable. Understanding and minimizing the noise floor is fundamental to receiver design.
Noise Floor Calculation
- Thermal noise power: N_thermal = kTB = -174 dBm/Hz + 10 log(BW_Hz).
- Receiver noise floor: N_floor = -174 + NF + 10 log(BW) dBm.
- Example: NF = 3 dB, BW = 10 MHz: N_floor = -174 + 3 + 70 = -101 dBm.
Noise Floor by Application
| Application | Typical Noise Floor |
|---|---|
| Spectrum analyzer (RBW=1 Hz) | -170 to -150 dBm |
| Cellular receiver (20 MHz) | -98 to -92 dBm |
| Wi-Fi receiver (20 MHz) | -95 to -90 dBm |
| Radar receiver (1 MHz) | -110 to -105 dBm |
Frequently Asked Questions
What is the noise floor?
The noise floor is the minimum detectable power level, determined by thermal noise plus receiver noise figure: N = -174 + NF + 10log(BW) dBm. It sets the lower limit of dynamic range and ultimate sensitivity.
How do you lower the noise floor?
Reduce noise figure (better LNA, lower-loss front-end components), narrow the bandwidth (reduces noise power proportionally), cool the receiver (cryogenic LNA), or use coherent integration (processing gain). Each 3 dB NF reduction lowers the floor by 3 dB.
What is kTB?
kTB is the fundamental thermal noise power in bandwidth B. k = Boltzmann's constant, T = temperature (290K standard), B = bandwidth in Hz. At room temperature: kTB = -174 dBm/Hz + 10log(BW). This is the absolute minimum noise in any receiver.